We are quantifying the time-course of phototransduction (intracellular voltage response and voltage clamped current response) in Limulus ventral photoreceptors. Linear sinusoidal input-output analyses and nonlinear systems identification will be used to describe photoresponse kinetics as they are affected by: 1) steady state adapting light level; 2) change in adapting light level; and 3) alteration of ionic or physiochemical environment of the cells.